This invention relates generally to digital equalizers, and more particularly to a digital equalizers designed so that a desired band-pass filter characteristic or band-elimination filter characteristic can be obtained by variably establishing the quality factor (Q), a center frequency, and gain.
Heretofore, a known method of designing and constructing a digital filter is by obtaining a function H(z) from the Z-transform of the transfer function H(s) which comprises a plurality of poles and zeros of the Laplace transformation form. This, for example, is seen in "IEEE Transactions on Audio and Electroacoustics", Vol. Au-16, No.3, Sep., 1968, Pages 350-391. But in the previous attempts to design a band-pass or band-elemination filter, an arbitary point was determined on the imaginary axis of the s-plane (complex-plane), the center frequency was determined by the distance from that point to the origin, poles were determined on a semi-circle on the left-hand side plane having that point as its center, and the cut-off frequency of the filter was determined by the radius of that semi-circle. Furthermore, the designing was done by positioning the zeros at the origin or infinity. Therefore, by this known method, not all types of filters can be designed, and was disadvantageous in that this designing method lacked general applicability. In addition, it was disadvantageous in that designing of the filter by arbitrarily varying the quality factor Q, the gain, the center frequency and the like, was difficult.